package com.hit.basmath.learn.others;

/**
 * 376. Wiggle Subsequence
 * <p>
 * A sequence of numbers is called a wiggle sequence if the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with fewer than two elements is trivially a wiggle sequence.
 * <p>
 * For example, [1,7,4,9,2,5] is a wiggle sequence because the differences (6,-3,5,-7,3) are alternately positive and negative. In contrast, [1,4,7,2,5] and [1,7,4,5,5] are not wiggle sequences, the first because its first two differences are positive and the second because its last difference is zero.
 * <p>
 * Given a sequence of integers, return the length of the longest subsequence that is a wiggle sequence. A subsequence is obtained by deleting some number of elements (eventually, also zero) from the original sequence, leaving the remaining elements in their original order.
 * <p>
 * Example 1:
 * <p>
 * Input: [1,7,4,9,2,5]
 * Output: 6
 * Explanation: The entire sequence is a wiggle sequence.
 * <p>
 * Example 2:
 * <p>
 * Input: [1,17,5,10,13,15,10,5,16,8]
 * Output: 7
 * Explanation: There are several subsequences that achieve this length. One is [1,17,10,13,10,16,8].
 * <p>
 * Example 3:
 * <p>
 * Input: [1,2,3,4,5,6,7,8,9]
 * Output: 2
 * <p>
 * Follow up: Can you do it in O(n) time?
 */
public class _376 {
    public int wiggleMaxLength(int[] nums) {
        if (nums.length == 0 || nums.length == 1) {
            return nums.length;
        }
        int k = 0;
        while (k < nums.length - 1 && nums[k] == nums[k + 1]) {  //Skips all the same numbers from series beginning eg 5, 5, 5, 1
            k++;
        }
        if (k == nums.length - 1) {
            return 1;
        }
        int result = 2;     // This will track the result of result array
        boolean smallReq = nums[k] < nums[k + 1];       //To check series starting pattern
        for (int i = k + 1; i < nums.length - 1; i++) {
            if (smallReq && nums[i + 1] < nums[i]) {
                nums[result] = nums[i + 1];
                result++;
                smallReq = !smallReq;    //Toggle the requirement from small to big number
            } else {
                if (!smallReq && nums[i + 1] > nums[i]) {
                    nums[result] = nums[i + 1];
                    result++;
                    smallReq = !smallReq;    //Toggle the requirement from big to small number
                }
            }
        }
        return result;
    }
}
